1Co 1:7-9 So that you come short in no gift, eagerly waiting for the revelation of our Lord Jesus Christ, (8) who will also confirm you to the end, that you may be blameless in the day of our Lord Jesus Christ. (9) God is faithful, by whom you were called into the fellowship of His Son, Jesus Christ our Lord.
The church at Corinth was not exactly one you would put at the top of your list if you were looking to enter the pastorate. They were full of infighting(Chpt. 1), immorality (Chpt. 5), Pride (all over), and Court battles (6), Divorce (7), Idolotry (10), Feminism (11), Abusing the Lord's Supper (11) and more.
But in the very opening of the book, Paul encourages them that Jesus will confirm them to the end. The idea of confirm is to establish or make sure of something. Some religions have a “confirmation service,” where they establish that a child, usually because of reaching a certain age, are now, “in the faith,” that they had been baptized into as an infant.
The basis for Jesus Christ confirming the Corinthians was not their goodness, but as you can see in verse nine, because, God is faithtful who called them into salvation (fellowship with God) through Jesus Christ.
What an iron clad case for perseverance of the saints.